In the field of applied electrochemistry, different design electrolyzers are used either for water and/or water solutions treatment, or for different product manufacturing. For instance, there are electrolyzers with flat electrodes pressed against the diaphragm (see the Author's certificate USSR No. 882944, 1979) or electrolyzers with coaxial cylindrical electrodes and a ceramic diaphragm between them (see the published patent application of Japan No 1-104387, 1989).
However, module electrolyzers are the most advanced because they provide the required production capacity by joining together the necessary number of modules. This reduces the design and production expenses of electrolyzers depending upon the required capacity and also helps to unify parts and reduce the time for assembly and disassembly of such electrolyzers.
The closest by the technical design and achieved result is a device for water treatment, executed by the module principle using electrochemical cells which contain coaxial cylindrical and rod electrodes and a coaxial ultrafiltration ceramic diaphragm made from materials using as their base zirconium, aluminum and yttrium oxides (see U.S. Pat. No. 5,427,667). The water treatment technical approach is chosen as a prototype.
The rod electrode is made with variable sections in the prototype and the diameter of its pin-ends is 0.75 of the diameter of its middle section. This allows for the improvement of hydraulic mode. In addition, dimensions of the electrodes and the diaphragm are specified in the formula, limiting their mutual change.
In the prototype, the rod and the cylindrical electrodes, as well as the diaphragm, are fixed in special dielectric bushings with channels for the treated water supply to be fed into and to be discharged from the rod electrode chamber. There are channels on the lateral surface of the cylindrical electrode, on its upper and lower parts, to supply and discharge treated water from the chamber of the cylindrical electrode. Water is treated while passing through the cell chambers from the bottom to the top.
Required production capacity devices are assembled with the number of cells by using special collectors, which are made either as a monolithic detail or special separate blocks for one cell and provided with joining and sealing tools. The order in which the electrodes connect to the poles of the power supply depends on the type of desired application.
The prototype treats water or water solution efficient at low energy consumption. The prototype is sufficiently simple in use, assembly and disassembly.
However, the prototype has disadvantages. Special collectors enlarge the size of the device, increase its hydraulic resistance and require the use of more powerful pumps. It also requires numerous joint parts and seals for them. The prototype does not work effectively under the different polarity of electrodes due to its constructive features. So when the rod electrode works as an anode, the coating wears outs rapidly in places of transition from the middle part to the pin ends (not including the holes whose share of the surfaces is small). All of the remaining place of transition is in the field of the cylindrical electrode and is subjected to an intensive influence of high intensity electric field (concentration of field in the places of changing form). It is not possible to control gas-filling of the treated solution in the prototype. The prototype device is also complicated in fabrication, because strict coaxiality for all details and the diaphragm are required. The fixation system for the rod electrode has difficulties in manufacture, due to the annular deepening on the internal surface of the bushings channels and placing seals in them.
The object of the present invention is to simplify the cell design and make it possible to place the required amount of cells in a smaller space; simplification of the fixation system for the elements of the cell; improving the reliability and increasing the lifespan of the cell due to the elimination the influence of a curved electrical field in the space between electrodes, as well as expansion of the functional abilities for the cell by making it possible to regulate the influence of gas-filling of the electrolyte on the electrochemical process.
This objective can be achieved when the electrochemical cell for water and/or water solutions treatment is made from vertical cylindrical coaxial parts such as an internal electrode of variable sections (the diameter of its end parts being not more then 0.75 of the diameter of its middle part), an external electrode and a coaxial ceramic diaphragm (made from materials having as their base zirconium oxides with additives of aluminum and yttrium oxides) which separates the inter-electrode space in the electrode chambers. The electrodes are made from material that is nonsoluble during electrolysis. The external electrode is installed in lower and upper dielectric bushings. Moreover there are slots on the butt-ends of upper and lower bushings, and the cell contains upper and lower dielectric collector heads, which have an axial channel. Moreover the heads are installed in the slots of bushings with the capability of turning. The diaphragm is fastened by elastic gaskets, which are placed in bushing slots. The diameter of the middle section of internal electrode is defined by the following formula: EQU 2M&lt;D&lt;4M
where:
D=the diameter of the middle section of the internal electrode in mm, and PA1 M=the distance between electrodes in min.
Depending on the execution and polarity of the electrodes, the length of the middle section of the internal electrode can be either shorter than the length of the external electrode on the value of 2M, or longer than the length of the external electrode on the value of not less than 2M. The preferred distance between electrodes is 2.8-3.3 mm. The internal electrode is fastened inside the heads by elastic gaskets placed in the axial head channels. The purpose of the channels in the lower and upper heads and in the lower and upper bushings is to supply and discharge treated water and/or solution into the internal and external chambers of the electrodes. The channels reach to lateral surfaces and are provided with outlets. The length of the external electrode can be varied from 50 mm to 240 mm depending on need.
Materials for the electrodes can be chosen from existing sources and the choice depends on the conditions and requirements for the design of the device. Should changing the polarity of electrodes not be required, titanium electrodes coated by titanium oxide and ruthenium oxide, or titanium electrodes coated by precious metals or manganese oxide or tin oxide or cobaltous oxide, can be used as an anode. Polished titanium or polished tantalum or polished zirconium coated by pyrographite or glass carbon or other coatings can be used as a cathode. If changing the polarity of electrodes is required, titanium electrodes coated by platinum or platinum-iridium can be used. It is possible to use different combinations of the materials listed above or other materials known in applied electrochemistry.
The diaphragm of the electrochemical cell is made from ceramics made from zirconium, aluminum and yttrium oxides, and can contain additives such as niobium oxide, tantalum oxide, titanium oxide, gadolinium oxide, hafnium oxide and others. Depending on the application, the diaphragm can be made as an ultrafiltration, a microfiltration or a nanofiltration. The forms of the diaphragm can be varied. The diaphragm can be a truncated cone with the conicity value 1:(100-1000) and a like thickness of walls equal to 0.4 mm-0.8 mm on the whole length of the diaphragm. The diaphragm can be installed in the cell either its big base facing downward or its big base facing upward.
The external (or internal) surface of the diaphragm can also be made as a cylinder, with the remaining surface (internal or external) made as a cone with the tonicity value 1: (100-1000). In this case, the wall thickness of one butt-end is 0.4 mm-0.5 mm and the wall thickness of the other butt-end is 0.7 mm-0.8 mm. The diaphragm is installed in the cell with its the butt-end with thickest wall either facing downward or facing upward.
The external and internal surfaces of the diaphragm can also be made as truncated cones with the conicity value 1: (100-1000). Moreover the cone tops are positioned at opposite end of the diaphragm and the thickness of the walls of one butt-end is 0.4 mm-0.5 mm and the thickness of the other butt-end is 0.7 mm-0.8 mm. The diaphragm is installed in the cell so that the butt-end with the thickest wall either is turned downward or is turned upward.
The internal and external surface of diaphragm can also be made as a cylinder with the wall thickness 0.4 mm-0.7 mm. Deviation from the geometric correct surface of the diaphragm should be not more than 0.05 mm in any part of its surface. The internal electrode is made either solid or hollow inside. The internal electrode can include several details, which are made from one or more materials, and are united by different methods (depending on materials), such as laser beam welding, vacuum welding, mechanically joining and the like. A thread is provided on the pin-ends of the internal electrode for adjustment of the head by manipulating washers and nuts.
Different combinations of internal electrode dimensions can be used, depending on the order in which the electrodes are connected with poles of the power supply. For instance, if the external electrode is connected with the negative pole of the power supply and the internal electrode is connected with the positive pole of the power supply, the length of the middle section of the internal electrode exceeds the length of the external electrode by a value of not less than 2M and the internal electrode is installed in the cell symmetrically to the external electrode. If the external electrode is connected with the positive pole of the power supply and the internal electrode is connected with the negative pole of the power supply, then the internal electrode middle section length is equal or less than the external electrode length on the value of 2M, and the internal electrode is installed in the cell symmetrically to the external electrode.
To provide strict coaxiality of electrodes in the cell, different variants are to be used for fastening of the internal electrode in the axial head channels depending on the dimensions of the electrodes.
When the length of the internal electrode exceeds the length of the external electrode by sufficient length, the axial head channel is contained within the variable section and the middle section of internal electrode with the big diameter forms a slot joint with the axial channels of the heads in which the elastic gaskets are placed. If the middle section of the internal electrode forms a slot joint with the axial channels of the upper and lower heads, then elastic gaskets are placed in the grooves of the middle section of the internal electrode. If the internal electrode is fastened by pin-ends, the axial head channel diameter is equal to the diameter of the pin-ends of the internal electrode; elastic gaskets are placed in grooves on the pin-ends of the internal electrode; or axial head channels having a diameter equal to the diameter of the internal electrode pin-ends and having an extension in the butt-ends; elastic gaskets are placed in this extension. In addition, the cell has clamping dielectric bushings which are also placed in this extension.
These improvements result in a better functioning and superior cell. Using coaxial electrodes and a diaphragm, and installing them in dielectric bushings and heads, allows for an optimal hydraulic regime and the simplification of the cell assembling. There is no need to drill a holes in the external cylindrical electrode, thus making it simple to manufacture. Because it is possible to turn the heads and regulate the outlet position, several cells can be assembled together compactly in one device.